1. Field of the Invention
The present invention relates to a radio base station apparatus, and a despreading processing apparatus therefor, in a radio communication system adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) systems.
2. Description of the Related Art
HSDPA (High Speed Downlink Packet Access) in UMTS (Universal Mobile Telecommunication System) is the specification for achieving higher speed data communication than in the third generation (3G) radio communication system such as W-CDMA, aiming at higher peak transmission speed in a downlink with a lower transmission delay. HSDPA has been standardized in “Release 5” specification, issued by the 3GPP (3rd Generation Partnership Project), a consortium for standardizing the 3G system specifications.
HSDPA has the following features: (1). Use of a single physical channel shared by a plurality of mobile units (user equipment: UE) in time division; (2) automatic selection of a higher speed modulation and coding scheme depending on radio wave conditions; (3) adoption of a hybrid ARQ in which retransmission request (ARQ) is combined with correction coding processing; and so on.
In contrast, HSUPA (High Speed Uplink Packet Access) is the specification for achieving higher data communication speed in the uplink of W-CDMA, which complements HSDPA for higher communication speed in the downlink. HSUPA has been standardized in “Release 6” specification issued by the 3GPP (3rd Generation Partnership Project), a consortium for standardizing the 3G system specifications.
According to the “Release 6” by the 3GPP, as shown in Table 1 listed below, the control channels required for processing HSDPA are DPCCH (Dedicated Physical Control Channel) and HS-DPCCH (High-Speed Dedicated Physical Control Channel), while the control channels required for processing HSUPA are DPCCH and E-DPCCH (Enhanced Dedicated Physical Control Channel). Further, the control channels required for processing both HSDPA and HSUPA are DPCCH, HS-DPCCH and E-DPCCH.
TABLE 1HSDPAandHSDPAHSUPAHSUPARequiredDPCCH + HS-DPCCH + E-DPCCH + HS-ControlDPCCHDPCCHDPCCH + E-ChannelsDPCCH
FIG. 1 shows a diagram illustrating a configuration of a conventional despreading processing unit of a control channel in a radio base station apparatus. In W-CDMA, a series of transmission information data is transmitted after being spread into wideband signals by means of a spreading code of higher rate, as compared to the symbol rate of information data. On the receiving side, by performing correlation detection using the spreading code which is identical to the spreading code used for spreading on the transmission side (the process concerned is referred to as despreading), the series of the transmission information data is regenerated. A proper spreading code is assigned to each UE, and each UE is identified by the above spreading code. Such the spreading code is constituted of the combination of two code types: a Channelization Code for identifying a physical channel, and a Scrambling Code for identifying each UE.
In FIG. 1, a despreading processing unit 10 in the radio base station apparatus includes a plurality (in FIG. 1, three) of despreading processing circuits 14A, 14B and 14C, and reception data are supplied from an input buffer 12 to each despreading processing circuit 14A, 14B, 14C. The signal being despread in each despreading processing circuit 14A, 14B, 14C is temporally stored in each of a plurality of output buffers 16A, 16B and 16C, which are provided corresponding to despreading processing circuits 14A, 14B and 14C, respectively, and then output therefrom. A scrambling code generation circuit 18 supplies a common scrambling code to each despreading processing circuit 14A, 14B, 14C, as will be described later.
In case of a 3.84 Mbps chip rate, for example, by operating each despreading processing circuit 14 at 3.84 Mbps×64=245.76 MHz, 64 resources can be processed in time division. Here, the number of resources is a unit of processing in each despreading processing circuit, which equals the number of channels taking finger into consideration. The finger is the number of paths to be synthesized at the time of RAKE reception, in which a plurality of paths are synthesized after timing and phases of the signals are adjusted for each path in a multipath environment. In case of three fingers for one channel, the number of resources becomes three, while in case of one finger for one channel, the number of resources becomes one.
The sum of the resources processed in each despreading processing circuit 14A, 14B, 14C becomes the number of processable resources N that can be processed in the overall despreading processing unit 10. In the example shown in FIG. 1, the number of processable resources N is 64×3=192.
FIG. 2 shows channel assignment in the conventional despreading processing circuits. Each despreading processing circuit 14A, 14B, 14C is provided for each control channel type. As shown in the figure, despreading processing circuit 14A is for dedicated use to DPCCH, despreading processing circuit 14B is for dedicated use to HS-DPCCH, and despreading processing circuit 14C is for dedicated use to E-DPCCH.
By supplying, to despreading processing circuit 14A, only a channelization code (which is actually supplied after being multiplexed with a scrambling code) corresponding to DPCCH, it becomes possible to use despreading processing circuit 14A as a dedicated circuit to the DPCCH processing. Similarly, by supplying only a channelization code corresponding to HS-DPCCH to despreading processing circuit 14B, and by supplying only a channelization code corresponding to E-DPCCH to despreading processing circuit 14C, it becomes possible to use despreading processing circuits 14B, 14C as a dedicated circuit to the HS-DPCCH processing, and a dedicated circuit to the E-DPCCH processing, respectively.
Further, when the number of processable resources in despreading processing unit 10 is N, the N resources are assigned to be equal to despreading processing circuits 14A, 14B, 14C provided for each control channel, and thus, each number of resources becomes N/3.
When processing HSDPA, both DPCCH despreading processing circuit 14A and HS-DPCCH despreading processing circuit 14B are used. At this time, because a proper scrambling code is given to one UE, both DPCCH despreading processing circuit 14A and HS-DPCCH despreading processing circuit 14B use a common scrambling code for one mobile unit UE (or user).
Also, when processing HSUPA, both DPCCH despreading processing circuit 14A and E-DPCCH despreading processing circuit 14C are used. As described above, because a single scrambling code is given to a single UE, both DPCCH despreading processing circuit 14A and E-DPCCH despreading processing circuit 14C use a common scrambling code for one mobile unit UE (or user).
Further, when processing both HSDPA and HSUPA, the entire DPCCH despreading processing circuit 14A, HS-DPCCH processing circuit 14B and E-DPCCH processing circuit 14C are used. Then, the entire DPCCH despreading processing circuit 14A, HS-DPCCH despreading processing circuit 14B and E-DPCCH despreading processing circuit 14C use a common scrambling code for one mobile unit UE (or user).
Namely, for each despreading processing circuit 14A, 14B, 14C, which processes N/3 resources in number, it is sufficient if one scrambling code generation circuit 18 is provided for generating N/3 common scrambling codes. Accordingly, as exemplarily shown in FIG. 1, scrambling code generation circuit 18 outputs, in time division, scrambling codes having the identical number to the number of resources (N/3=64), in synchronization with the processing in each despreading processing circuit 14.
Although a channelization code generation circuit is omitted in the figure, actually, a channelization code is supplied to each despreading processing circuit after being multiplexed with the scrambling code. Each channelization code generation circuit is provided for each control channel type.
In the official gazette of the Japanese Unexamined Patent Publication No. 2005-130,246 (Patent document 1), there has been disclosed a radio receiver unit in which path tables for finger assignment in RAKE synthesis are set separately to fit to each channel characteristic, and the finger is assigned independently of each channel, thereby performing RAKE synthesis to demodulate a received radio signal.
In the above configuration shown in FIG. 1, when processing both HSDPA and HSUPA, the entire despreading processing circuits 14A, 14B, 14C are used. However, when processing HSDPA, E-DPCCH despreading processing circuit 14C is unused, and also, when processing HSUPA, HS-DPCCH despreading processing circuit 14B is unused. Therefore, the processing capacity corresponding to the number of resources processable in an unused despreading processing circuit becomes wasteful, and the use efficiency of the despreading processing circuit is degraded.